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p= 0.63 We randomly select n= 14 Americans to survey and we want to draw a histogram of the binomial distribution for that survey.
Are you a sports fan? YES NO |
Recall that in a binomial experiment with n independent trials there are two possible outcomes, a success and a failure. The probability of success, which is the probability of a positive answer, equals p= 0.63. Conversely, the probability of a failure is denoted as 1- p. 1- p=1- 0.63 Now, for a binomial experiment, the probability of exactly k successes can be written with the following formula. Note that k successes is equivalent to k people saying they are sports fans. P(k successes ) = _nC_kp^k(1-p)^(n-k) In this formula, _nC_k can be expanded using a formula for the number of combinations. _nC_k ⇔ n!/k!(n-k)! Now, let's substitute n= 14 and p= 0.63 into our formula and simplify. P(k) = _(14)C_k( 0.63)^k(1- 0.63)^(14-k) ⇓ P(k) = _(14)C_k(0.63)^k(0.37)^(14-k) We need to calculate the probability of k successes for each possible value of k. Note that there can be as many as k=0,1,2,..., 14 successes in this trial. Let's use a table for this.
Number of Successes k | P(k) | Simplify | Use Calculator |
---|---|---|---|
0 | _(14)C_0(0.63)^0(0.37)^(14- 0) | 1(1)(0.37)^(14) | 0.000000 |
1 | _(14)C_1(0.63)^1(0.37)^(14- 1) | 14(0.63)(0.37)^(13) | 0.000021 |
2 | _(14)C_2(0.63)^2(0.37)^(14- 2) | 91(0.63)^2(0.37)^(12) | 0.000237 |
3 | _(14)C_3(0.63)^3(0.37)^(14- 3) | 364(0.63)^3(0.37)^(11) | 0.001619 |
4 | _(14)C_4(0.63)^4(0.37)^(14- 4) | 1001(0.63)^4(0.37)^(10) | 0.007582 |
5 | _(14)C_5(0.63)^5(0.37)^(14- 5) | 2002(0.63)^5(0.37)^9 | 0.025821 |
6 | _(14)C_6(0.63)^6(0.37)^(14- 6) | 3003(0.63)^6(0.37)^8 | 0.065949 |
7 | _(14)C_7(0.63)^7(0.37)^(14- 7) | 3432(0.63)^7(0.37)^7 | 0.128334 |
8 | _(14)C_8(0.63)^8(0.37)^(14- 8) | 3003(0.63)^8(0.37)^6 | 0.191200 |
9 | _(14)C_9(0.63)^9(0.37)^(14- 9) | 2002(0.63)^9(0.37)^5 | 0.217038 |
10 | _(14)C_(10)(0.63)^(10)(0.37)^(14- 10) | 1001(0.63)^(10)(0.37)^4 | 0.184776 |
11 | _(14)C_(11)(0.63)^(11)(0.37)^(14- 11) | 364(0.63)^(11)(0.37)^3 | 0.114407 |
12 | _(14)C_(12)(0.63)^(12)(0.37)^(14- 12) | 91(0.63)^(12)(0.37)^2 | 0.048700 |
13 | _(14)C_(13)(0.63)^(13)(0.37)^(14- 13) | 14(0.63)^(13)(0.37) | 0.012757 |
14 | _(14)C_(14)(0.63)^(14)(0.37)^(14- 14) | 1(0.63)^(14)(1) | 0.001551 |
_(14)C_0= 14!/0!(14-0)!
Subtract terms
Cancel out common factors
Simplify quotient
0!=1
a/a=1
P(k ≥ 7) = P(7) + P(8) + ... + P(14) Let's use the probabilities we found in Part A.
k | P(k) |
---|---|
0 | 0.000000 |
1 | 0.000021 |
2 | 0.000237 |
3 | 0.001619 |
4 | 0.007582 |
5 | 0.025821 |
6 | 0.065949 |
7 | 0.128334 |
8 | 0.191200 |
9 | 0.217038 |
10 | 0.184776 |
11 | 0.114407 |
12 | 0.048700 |
13 | 0.012757 |
14 | 0.001551 |
Let's add the probabilities. This will give us our answer. & 0.128334 +& 0.191200 +& 0.217038 +& 0.184776 +& 0.114407 +& 0.048700 +& 0.012757 +& 0.001551 =& 0.898763 We have that the probability that at least 7 Americans out of the group are sports fans equals approximately 0.899=89.9 %.